1. Field of the Invention
The presently disclosed subject matter relates to a heterogeneous catalyst and use of the heterogeneous catalyst for transesterification.
2. Description of the Related Art
Transesterification is the reversible chemical reaction process of exchanging the organic group of an ester with the organic group of an alcohol. Transesterification processes became commercially popular in the 1940s as researchers explored ways to more readily produce glycerol (also called glycerin, glycerine and propanetriol) used in explosives manufacture during World War II. Currently, transesterification is an important step in industrial processes such as production of: acrylates from methymethacrylate, polyethylene terephthalate (PET) polymer manufacturing from ethylene glycol and either dimethyl terephthalate or terephthalic acid, and alkyl esters. Of particular current commercial interest is the transesterification of alcohol with triglyceride esters contained in oils and fats (primarily vegetable oils and animal fats) to form fatty acid alkyl esters and glycerin. These esters find commercial use as biodiesel fuel and biolubricants.
Catalysts known to facilitate the transesterification reaction include mineral acids and bases, metal alkoxides, non-ionic bases and lipase enzymes. These catalysts include homogeneous species which are soluble in reactants and/or products and heterogeneous species which are solids and insoluble in reactants or products.
Alkaline metal alkoxides (e.g., CH3ONa for methanolysis) and alkaline metal hydroxides (NaOH and KOH) are catalysts for the homogeneous transesterification reaction. These catalysts are soluble in reactants and products and thus require extensive post-reaction treatment including product neutralization, salt removal and water wash to produce commercially acceptable products. These are nontrivial processes and costly to install, maintain and operate. Homogeneous enzymatic transesterification using lipase has been utilized for conversion of triglycerides to biodiesel, since the byproduct glycerin can be purified by flashing off the excess alcohol from the products. However, processing time can be lengthy for acceptable conversion of triglycerides and product clean-up costs are high to make commercial grade products.
Replacement of the homogeneous catalyst with heterogeneous catalyst has been commercialized notably with the Esterfip-H® process licensed by Axens and the ENSEL® process licensed by Benefuel. These heterogeneous catalyst processes can reduce post-reaction processing, but require reaction operating temperatures of 150 degrees C. to 250 degrees C. and alcohol partial pressure as high as 300 to 400 psi for the manufacture of biodiesel alkyl esters. These heterogeneous catalyst reactions must be carried out in fixed bed reactors due to the severity of the process conditions.
Improvements in this field of technology are desired to reduce the operating severity and costs of the transesterification reaction regime as well as the subsequent process clean-up and product purification steps. Improvements are also desired which allow use of new technology in existing or readily modified commercial facilities.